The present invention relates to a method of manufacturing cylinder apparatus such as hydraulic shock absorbers.
Examples of cylinder apparatus include a cylinder type hydraulic shock absorber that is attached to a suspension system of a vehicle, e.g. an automobile. Such a shock absorber generally has the following structure. A piston connected with a piston rod is slidably fitted in a cylinder having a fluid sealed therein. In response to a stroke of the piston rod, the piston slidingly moves in the cylinder, causing a flow of fluid. The flow of fluid is controlled to generate damping force by a damping force adjusting mechanism comprising an orifice, a disk valve, etc.
In a hydraulic shock absorber disclosed in Japanese Patent Application Publication No. 2006-38097, a back-pressure chamber (pilot chamber) is formed at the back of a disk valve constituting a damping force generating mechanism. A part of the flow of fluid is introduced into the back-pressure chamber to apply the pressure in the back-pressure chamber to the disk valve in the direction for closing the valve. The pressure in the back-pressure chamber is controlled with a pilot valve to control the valve-opening operation of the disk valve. With this arrangement, it is possible to increase the degree of freedom for adjusting damping force characteristics.
In the shock absorber disclosed in Japanese Patent Application Publication No. 2006-38097, a ring-shaped seal member made of an elastic material, e.g. rubber, is fixed to the outer periphery of the rear side of the disk valve by vulcanization bonding or the like, and the seal member is slidably and fluid-tightly fitted to a cylindrical portion of a cylindrical member, one end of which is closed, and which is disposed at the back of the disk valve, thereby forming a back-pressure chamber.
The present inventors measured the damping force characteristics of shock absorbers using a disk valve having a ring-shaped seal member fixed to one side thereof as stated above, and found that the damping force characteristics vary for each shock absorber. The inventors investigated the cause of variations in damping force characteristics, and found that there are variations in flatness of the disk valve of each shock absorber.